Metallurgical product and process



nited States This invention relates to metal powders and in particular to metal powders consisting predominantly of nickel which are suitable for the manufacture of shaped articles by cold pressing followed by heating and subsequently pressing or rolling at temperatures on the order of 1000-1100 C.

In the conventional production of nickel from its ore by hydrochemical methods the nickel is obtained in the form of a very fine grained powder. To remelt this powder to make shaped objects such as tubes, sheets or strips presents a number of metallurgical problems and is very expensive. It has therefore been proposed to shape the powder itself using powdered metal methods; i.e. by first cold prccompressing the powder, followed by hot or cold rolling to form sheets or strips or extrusion to form tubes or bars. However, it has been found that the products formed in this way from the chemically produced powder have mechanical properties which are so poor that they complicate or entirely prevent their subsequent processing to form useful items.

It has now been found that the reason for these poor physical properties is that the individual grains of the nickel powder contain on the order of 0.2% oxygen and 0.008% sulfur, and that upon heating before but working they become covered with an extremely thin liquid skin or film consisting of a nickel sulfide-nickel oxide slag. This film prevents the welding of the nickel grains to one another upon hot rolling or pressing.

In accordance with the invention this undesirable effect is eliminated by incorporating in the nickel powder a minor amount of a metal powder having a higher ailinity for oxygen and possibly also for sulfur than has nickel and whose oxides and sulfides, even as a mixture, will not form a slag melting at the processing temperature. In this manner the melting point of any slag which might form is raised above the temperature at which the powder is worked, and thus no liquid slag film can form on the metal grains. The oxides and sulfides formed with the admixed metal powder remain in the nickel in solid form and in a state of very fine subdivision. They are so fine they cannot be recognized in a polished section.

The invention therefore comprises a metal powder suitable for the manufacture of shaped articles by operations including a preliminary cold pressing followed by a hot working, said powder comprising predominantly nickel and containing a minor amount of a metal capable of combining with oxygen and sulfur present in the nickel and of forming a slag having a melting point of at least 1100" C.

The metal powder admixed with the nickel in accordance with the invention may be any powder having greater ailinity for oxygen and sulfur than nickel, and which will not form a slag at working temperature. Aluminum, magnesium and mixtures thereof have been found particularly suitable. They will normally be used in a proportion of from about 0.05% to about 1% of the weight of the powder, preferably from about 0.2 to about 0.3% of the Weight of the powder.

The invention will be further illustrated by the following specific example which is intended only as an illustration of the invention and is not to be taken as in atent 3,078,157 Patented Feb. 19, 1963 any way restricting the invention beyond the scope of the appended claims.

Example A batch of nickel powder produced industrially by the conventional wet chemical process and containing 0.009% by weight sulfur and 0.21% by weight oxygen was divided into two parts. One part was mixed with 0.3% powdered magnesium. The other part received no additive. Both parts were cold compressed in a press, mold at a pressure of 5 tons (metric)/cm. to form cylindrical blanks each having a diameter of mm., a density of 7.0 and a weight of 20 kg. These blanks were then extruded in an extrusion press at a temperature of 1050 C. to form tubes having a diameter of 65 mm. and a wall thickness of 8 mm. The products were then tested for tensile strength and elongation. The results are tabulated below:

Tube formed Tube formed without with 0.3%

additive Mg added Tensile strength (kg/mm. 13 55 Elongation (percent) 1 40 It is thus evident that articles prepared in accordance with the present invention are greatly improved compared to those obtained using prior metal powder techniques and reach the properties of articles made by smelting the nickel. In fact it has been found that in its resistance to heat, as indicated by the hot tensile test at 550 C., tubing made according to the invention shows a value of 31.5 kg/mmfi, 55% higher than normal tubing.

it will be understood that the invention is not restricted to metal powders consisting solely of nickel, but is useful in processing mixtures of nickel powder and other metal powders such as Monel metal and the like, to form articles of nickel alloys.

We claim:

1. A metal powder suitable for the manufacture of shaped articles by operations including a preliminary cold pressing followed by a hot working, said powder consisting essentially of nickel and between about 0.05 and about 1% by weight of a metal which is capable of combining with oxygen and sulfur present in the nickel and of forming a slag having a melting point of at least 1100 C., selected from the group consisting of aluminum, magnesium and mixtures thereof.

2. The powder claimed in claim 1 wherein the metal is capable of forming a slag having a melting point over 1300 C.

3. The powder claimed in claim 1 wherein the metal capable of combining with oxygen and sulfur comprises between about 0.2 and about 0.3 percent by weight of the powder.

4. A method for forming shaped articles from a powder consisting essentially of nickel and containing sulfur and oxygen as impurities, which comprises adding to said powder between about 0.05% and about 1% by weight of a metal capable of combining with said sulfur and oxygen and of forming a slag with sulfur and oxygen having a melting point of at least about 1100 C., said metal being selected from the group consisting of aluminum, magnesium and mixtures thereof, cold pressing the 3 mixture and but working the pressed mixture at a temperature of about 1000 C. to about 1100 C.

5. The method claimed in claim 4 'wherein the metal added is capable of forming a slag with oxygen and sulfur having a melting point over about 1300 C 6. The method claimed in claim 4 wherein the amount of the metal added is between about 0.2 and about 0.3 percent of the weight of the powder.

4. References Cited in the file of this patent UNITED STATES PATENTS 2,319,373 Tormyn May 18, 1943 2,441,126 Kurtz May 11, 1948 2,471,630 Kurtz May 31, 1949 

1. A METAL POWDER SUITABLE FOR THE MANUFACTURE OF SHAPED ARTICLES BY OPERATIONS INCLUDING A PRELIMINARY COLD PRESSING FOLLOWED BY A HOT WORKING, SAID POWDER CONSISTING ESSENTIALLY OF NICKEL AND BETWEEN ABOUT 0.05 AND ABOUT 1% BY WEIGHT OF A METAL WHICH IS CAPABLE OF COMBINING WITH OXYGEN AND SULFUR PRESENT IN THE NICKEL AND OF FORMING A SLAG HAVING A MELTING POINT OF AT LEAST 1100* C., SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, MAGNESIUM AND MIXTURES THEREOF. 